The present invention relates to a storage system having a plurality of interfaces. More specifically, the present invention relates to a hybrid-type storage system allowing accesses to data to be made by both a SAN (Storage Area Network)-interface command and a NAS (Network Attached Storage)-interface command.
In recent years, accompanying the growth of the application field of the information system and the progress of the distribution of processing of a computer system, the number of hosts controlled at one site increases substantially. With the number of such hosts increasing, a problem of an increased cost of managing storage systems is raised. In particular, if storage systems of distributed hosts are managed individually, the capacity required by each storage system as a capacity necessary for carrying out operations is difficult to estimate in advance. Thus, if there is a need to increase the capacity, it is necessary to newly install an additional storage system for each individual host. In consequence, the management cost increases.
As technologies for solving the above problem, SAN and NAS techniques are used. It is an object of both the technologies to consolidate storage systems owned individually by distributed hosts. Due to different characteristics of the technologies, however, they are applied to different fields.
The SAN technology is a technology for connecting a plurality of storage systems and a plurality of hosts to each other by using a network dedicated for communications between the hosts and the storage systems in order to implement I/O operations having a high speed and a small latency. In accordance with the SAN technology, an I/O operation between a host and a storage system is carried out in block units. A block is a fixed-length data management unit identified by an address. A block is obtained as a result of dividing the capacity of a storage system into smaller portions each having a predetermined size corresponding to the fixed length. A database is a representative of applications for which the I/O operation carried out in block units is suitable. By consolidating a plurality of database volumes into a single storage system so as to allow their management to be executed in a uniform manner, the management cost of the computer system can be reduced. In addition, the SAN technology provides a dedicated network having high reliability and allows communications to be carried out with a high degree of efficiency. Thus, the SAN technology can also be used as a technique providing an effective communication path for transmitting data in volume units. The transmission of data in volume units is carried out to copy a volume to a remote storage system for the purpose of making a backup for the volume and for the purpose of providing a countermeasure to against accidents on the volume.
On the other hand, the NAS technology is a technique providing a storage system having a file-server function for rendering file services to a plurality of hosts existing in a LAN (Local Area Network). I/O operations between the storage system provided by the NAS technology and the hosts are carried out in file units. In general, a file is identified by using an identifier, which is a character string. A file is a data management unit having a variable length. A representative of applications for which I/O operations carried out in file units are suitable is an application of allowing a plurality of hosts to share a file. By adopting the NAS technology, it is possible to implement a system allowing a plurality of web servers to share a service of the same content and a system allowing a plurality of office PCs to share a text.
As is obvious from the above description, the SAN and the NAS technologies are mutually complementary. These technologies have led to formation of an idea of further reducing the management cost by integration of storage systems conforming to the SAN with the NAS technologies into a single storage system. In accordance with technologies disclosed in non-patent reference 1 and patent reference 1, which are described below, by providing a control program of a storage system as a control program allowing control of both the SAN and the NAS storage systems to be executed, a storage system conforming to both the SAN and the NAS technologies can be implemented. A storage system applying these technologies has SAN and NAS interfaces and allows a storage capacity thereof to be apportioned to the SAN and the NAS interfaces with a high degree of freedom.
It is to be noted that aforementioned patent reference 1 is Japanese Patent Laid-open No. 2003-162439. On the other hand, non-patent reference 1 cited above is a reference authored by Stephen Daniel with a title of “Converging SAN and NAS Storage—A Comparison of Unified and Gateway Solutions,” Network Appliance Inc., White Paper, October 2002.